The prevalence of and risk factors for Atention Deficit Hyperactivity Disorder are being investigated in a population-based study carried out in Johnston County, North Carolina. Through the cooperation of the Johnston County schools, all elementary school age children in the county were studied. With parental permission, teachers completed behavior rating evaluations for children in their classroom. All children classified as potentially having ADHD according to teacher responses or reported by parents to be taking medications were eligible for further study, along with a random sample of all other children. Parent interviews obtained information on child behavior, prenatal and childhood exposures, parental occupational exposures and other factors potentially related to risk for ADHD. The pilot study combined parent and teacher information to estimate the prevalence of ADHD among elementary school children. Two-stage screening used DSM-IV criteria. Teachers completed behavior-rating scales on all children and then parents of potential cases were administered a structured telephone interview. 362 of 424 (85%) children in grades 1-5 in four schools were screened. We estimated the prevalence of medication treatment for attention deficit-hyperactivity disorder (ADHD) among elementary school children in a North Carolina county. We asked parents of 7333 children in grades 1 through 5 attending 17 public elementary schools whether their child had ever been given a diagnosis of ADHD by a psychologist or physician and whether their child was currently taking medication to treat ADHD. The primary aims of the project are 1) to describe the prevalence of ADHD and how it varies by age, race, gender, and SES, 2) to test the hypothesis that preterm and post-term births are at higher risk for ADHD and 3) to evaluate the role of maternal smoking, maternal occupation, maternal alcohol consumption and pregnancy complications as risk factors for ADHD. In the results for the first year of the study, according to parental reports, 43 children (12%) previously had been diagnosed with ADHD by a health professional. Thirty-four children (9%) were taking ADHD medication. Forty-six children met study case criteria for ADHD based on combined teacher and parent reports. Of 46 cases, 18 (39%) had not been previously identified. However, 8 previously-diagnosed children did not meet case criteria. After adjusting for non-response, the estimated prevalence was 16% These data suggest that the DSM-IV prevalence of ADHD has been substantially underestimated, although the true prevalence in this population may be less than the 16% estimated in this pilot study. In the prevalence of medication results, parents of 6099 children (83%) responded. By parental report, 607 children (10%) had been given an ADHD diagnosis, and 434 (7%) were receiving ADHD medication treatment (71% of the diagnosed children were receiving medication). Treatment rates varied by sex, race/ethnicity, and grade. If treatment patterns observed in this study are representative, the public health effect of ADHD may be underestimated.